A number of zirconium compounds have been used to oligomerise ethylene to alpha olefins, generally associated with various other ligands.
Examples are the use of zirconium halides associated with esters, ketones, ethers, amines, nitrites, anhydrides, acid chlorides, amides or aldehydes, described in United States patent U.S. Pat. No. 4,855,525 and International patent application WO 91 02707, or the use of the same zirconium halides associated with ligands selected from the group formed by sulphur-containing, phosphorous-containing or nitrogen-containing compounds, described in European patents EP-A-0 241 596 and EP-A-0 328 728.
The products obtained with the catalytic formulae given above are principally constituted by alpha olefins with a chain length of between C.sub.10 and C.sub.18.
U.S. Pat. No. 5,345,023 describes a process for producing light alpha olefms, principally 1-butene, 1-hexene, 1-octene and 1-decene, by oligomerising ethylene, using a catalytic composition obtained by mixing a zirconium compound with an organic compound selected from the group formed by acetals and ketals and with a chlorine-containing or bromine-containing aluminium hydrocarbyl compound. The teaching of this patent is included in the present application.